(1) Field of the Invention
The present invention relates to a mold for molding a glass and to a method of producing the same. More specifically, the invention relates to a mold which is used for molding a parison from a molten glass gob, and which features long life, excellent moldability and smoothness of the glass molded articles.
(2) Description of the Prior Art
In a step of molding a glass, masses of glass melted at a high temperature are thrown into a mold (blank mold and neck ring). In this case masses of glass do not often completely flow into the mold or wrinkles develop due to frictional resistance relative to the mold. In order to prevent this as well as to easily remove the glass molded into the shape of a parison from the mold, an oil (swabbing compound) containing graphite is applied onto the inner surfaces of the mold at intervals of several tens of minutes. However, since the mold is usually heated at a temperature as high as about 500.degree. C., oil soot generates to deteriorate the working environment. Moreover, the graphite applied in excess amounts adheres to the surfaces of the glass container causing the products to be fouled and deteriorating the yields of the products.
In order to solve these problems, there have been proposed a variety of lubricating/parting agents to substitute for the swabbing compounds. For instance, Japanese Laid-Open Patent Publication No. 127111/1976 discloses a lubricating/parting agent used in an apparatus for producing glass containers, comprising 5 to 30% by weight of graphite or a mixture of graphite and a boron nitride, 5 to 30% by weight of at least one compound selected from the group consisting of aluminum biphosphate, aluminum primary phosphate and magnesium biphosphate, and 40 to 90% by weight of an aqueous solution containing acid.
In order to impart lubricating/parting property to the inner surface of the mold, furthermore, Japanese Laid-Open Patent Publication No. 10207/1974 discloses a mold for molding glass articles in which a nickel film 10 containing phosphorus in an amount of 3 to 13% by weight is nonelectrolytically plated onto the inner surfaces of the mold maintaining a thickness of 5 to 300 .mu.m.
Japanese Laid-Open Patent Publication No. 100027/1988 filed by the present inventors discloses a mold for molding a glass wherein the inner surfaces of the mold are coated with a film in which are dispersed graphite granules using nickel or a nickel-based alloy comprising chiefly nickel as a matrix.
However, the former lubricating/parting agent is yet poor in regard to heat resistance and abrasion resistance, and has a life of about 1 to 3 days. The alloy coating method mentioned above is excellent in regard to durability of the film but still has a problem with respect to lubricating property which is very poor.
The latter nickel film dispersed with graphite exhibits excellent lubricating property and durability compared with those of the above prior art, but still tends to develop fine scars on the glass surfaces. The scars on the surface of the molded glass gradually increase after being used for extended periods of time.
That is, the film of the graphite-dispersed nickel plating exhibits excellent lubricating property possessed by graphite and excellent heat resistance and abrasion resistance possessed by nickel. In effecting the dispersive plating, however, the nickel layer plated on the surfaces of the mold greatly grow like granules in a direction perpendicularly to the surface of the mold. Thus, scars develop in the surface of the glass being caused by nickel that undergoes granular growth.